A large number of neurological and neurodegenerative diseases are known, many of which are presently not curable. All common neurodegenerative diseases are characterized by the misfolding, aggregation, and/or deposition of specific proteins in the brain. These diseases include medical conditions such as Parkinson's disease (PD), Alzheimer's disease (AD), Transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt-Jakob disease (CJD), senile dementia, AA amyloidosis, arteriosclerotic dementia, Huntington's disease (HD), cerebral thrombangitis obliterans, dementia with Lewy bodies (DLB), multiple system atrophy (MSA) and many others. Type 2 diabetes is yet another disease whose pathogenesis involves ordered protein aggregation.
In the case of TSEs, the misfolded protein, which forms aggregates, is called “prion”, which is derived from “proteinaceous” and “infectious”. Therefore TSEs are also called prion diseases. The central event in the pathogenesis of TSEs is the conversion of the cellular prion protein PrPC into the pathological PrPSc isoform, which accumulates into large protein aggregates. Prions propagate by transmitting a misfolded protein state. When a prion enters a healthy organism, it induces existing, properly folded proteins to convert into the disease-associated, prion form. These newly formed prions can then go on to convert more proteins themselves; this triggers a chain reaction that produces large amounts of the prion form. All known prions induce the formation of an amyloid fold, in which the protein polymerizes into an aggregate consisting of tightly packed beta sheets. Amyloid aggregates are fibrils, growing at their ends, and replicating when breakage causes two growing ends to become four growing ends. This altered structure is extremely stable and accumulates in infected tissue. The propagation theory described for the prion protein may also apply to amyloid formation in other protein misfolding disorders (PMDs).
Another class of neurodegenerative diseases, the so-called synucleinopathies are characterized by intracellular accumulation of protein aggregates, oligomers, protofibrils and fibrils, containing mainly α-synuclein. In the cases of synucleinopathies it is believed that the pathological effects on nerve cells are induced by the formation of oligomeric aggregates of α-synuclein and the subsequent formation of membrane pores. Examples of synucleinopathies are Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy.
In fact, protein conformation changes associated with the pathogenesis of most PMDs result in the formation of abnormal proteins that are rich in β-sheet structure, partially resistant to proteolysis, and have a high tendency to form larger-order aggregates, similar to prions. Amyloid formation depends on the slow interaction of misfolded protein monomers to form oligomeric nuclei, around which a faster phase of elongation takes place. The ability of oligomeric species to seed their own growth is analogous to the self-propagating activity of prions.
These oligomers that occur during the aggregation are described in literature as to be the main toxic agent leading to cell dysfunction and cell death. One possible mechanism leading to cell death is membrane perforation caused by the protein aggregates. To treat the disease caused by the protein aggregation in the tissue of the patient, the protein aggregation has to be prevented, decreased or, at best, removed from the tissue.
This can be achieved in the case of prion diseases by a therapeutic approach targeted at interfering with the formation and amplification of the infectious protein (PrPSc). Evidence derived from cell culture and in vivo studies suggests that once formation of PrPSc is inhibited, clearance of PrPSc can take place. Thus, this therapeutic strategy can also be effective late in the incubation period and even after manifestation of clinical signs of disease, which is essential to be of use in addressing human prion disease.
There are a number of compounds which have been shown to be effective in interfering with PrPSc amplification in vitro such as acridin derivatives, Congo Red, porphyrins/phthalo-cyanines, Cp-60, beta-sheet breaker peptides and variants of PrP. However, none of these compounds have so far been used successfully for disease treatment or as lead compounds for developing compounds with increased therapeutic potency and pharmacological properties.
In WO2010/00372, compounds were disclosed, which have been shown to be effective in inhibiting aggregation of proteins. A broad screen based on a combination of scanning for intensely fluorescent targets (SIFT) and cellular assays measuring the amount of aggregation of α-Synuclein (PD) and prion protein (CJD). In this screen 3,5-diphenyl pyrazole (DPP) compounds turned out to be a highly active scaffold that could be easily modified by organic synthesis. An array of around 250 compounds in this class was synthesized and the compounds were assessed for oral availability and efficacy in animal models mimicking the various mentioned diseases (AD, CJD, PD). The compound termed “anle138b” having the following structure:
